Any major human character. Seriously. Pick one. The only good human nowadays is a dead one. This is coming from a multi-faction player. The humans sit atop their attention-absorbing throne of pure boredom. Alliance needs more Dwarf.

Taran Zhu. ya when garrosh nearly killed him in the 5.4 trailer, he should have just finished the job.
Jaina - we know shes gonna lose her shit one of these days of the month and boom! bye bye kalimdor.
Koltira Deathweaver- if he is still alive stuck in UC somewhere just finish the job, hes a traitor anyway.
Thrall - just cause we've seen enough of him for now, maybe have him take a vacation somewhere.
Gallywix/Tyrande/Velen/Genn Greymane - most of the useless characters that dont add anything interesting to the plot.

Ill set up a scenario for mine because killing off characters should be something to remember them by.

After fighting the Warlords, Thrall decides to go to Stormwind and ask Varian to make a formal alliance between the 2 nations, to work together and possibly one day become a unified force. After 2 days of touring Stormwind and meeting the people, they begin their talks. Besides Varian, Jaina, Anduin, Vereesa, Kalec and Kadger are present at the meeting. After hours of discussion, they finally come to an agreement, Jaina is so happy, Anduin is cheerful, Vereesa thinks of how Rhonin would be happy, Kalec nods and Kadger says "Do you sense that?".

Stormwind is suddenly assaulted by a large object in the sky. Explosions throughout the city as the dark energy falls onto buildings below. Griffon riders take to the air, but are caught in some sickly mist, a miasma and fall to their deaths. The ships in the port and the Airship in the hangar begin to retaliate, their cannons blast away at the underside of the floating structure. Suddenly dark beings jump from the ledge and make it to the gunship. The gunships deck goes dark as a black fog envelopes it, the cannons stop firing and then after a few moments, the airship starts to turn to the port and falls rapidly. The airships smashes into the docks and explodes, destroying most of the ships in the port. A figure in dark robes appears at the ledge, pulls back his hood to reveal a tall male human with pale skin and lifeless white hair. he raises his hands and clasps them together. The bottom of the structure bursts apart and massive amounts of miasma falls from it and envelopes the entire city.

Thrall and the gang are in the garden and thrall quickly summons the wind to surround them, but it's no use. The miasma mixes in and encloses in on them. Jaina and Kadgar summon a barrier. The world goes dark and for a few minutes all they can do is listen to the screams, but eventually it quiets down. Anduin is praying hard, begging the light to save them, but it does not answer him. They even tried teleporting, but it did not work. This wasn't just some plague, but a strong magic. Eventually the barrier starts to erode and the miasma starts to seep in. They're all ready to embrace death, praying for a Metzen miracle...

10 days later, the miasma has disappeared. Only the dead walk Stormwind. In the Garden 7 bodies can be found in a circle, with ice piercing each ones head. They took their own lives.

And that's how I would kill off Thrall and the annoying Alliance Human leaders(Vereesa, Kalec and Kadgar are all alliance and especially stormwind characters)

Tyrande, I hate that slut. Like hell, I hate all night elves but she pisses me off the most, And malfurion lol, Malfurion is so blind of love that he can't see that Tyrande has done some horrible things in her life, Like releasing Illidan, But heck no, when Maiev captured him and found out that tyrande was alive he was like. Screw you Tyrande! Imma save my loved one and fight alongside the one of the people I hate the most in my life. Lol, Tyrande even blames Maiev for releasing Illidan, Not that but she thinks she's better than everyone else. I'd kill dat slut instantly If I had the powers to do so. Honorable mention: sylvanas, I don't really have anything against her at all, but it would be interesting to see who the undead Racial leader would be if she dies.

King Varian Wrynn. I hate the concept of "High King of Alliance". Wrynn is just stealing screen time frorm interesting alliance leaders like Tyrande, Velen, Moira, Greymane and Mekkatorque. He is not a likeable character. He is just pompous and bossy. And Alliance could be so much more than just humans.